1. Field of Invention
This invention relates to fast curing, two part adhesives and to articles bonded therewith. The curable adhesives described herein comprise a first part component of free radical initiated polymerizable acrylic monomers and a diazonium salt. A second part, which is brought in contact therewith just prior to use, comprises a condensation reaction product of an aldehyde and a primary or secondary amine to induce the free radical decomposition of the diazonium salt.
2. Description of the Prior Art
Disclosed in the prior art are many curable adhesive compositions which cure or set by free radical polymerization of ethylenically unsaturated polymerizable monomers. The prior art relative to curable adhesives discloses free radical initiators which are of the organic peroxy or hydroperoxy type including peresters or peracids. Especially useful are the peresters and peroxides such as t-butyl perbenzoate and cumene hydroperoxide. Also disclosed in the prior art are curing adhesive compositions employing aldehyde-amine condensation reaction products as free radical accelerators and primers for these peroxy compounds. Also disclosed in the prior art are anaerobic curing adhesive compositions employing diazonium salts as latent polymerization catalysts.
U.S. Pat. No. 3,591,438 to Toback et al is directed to adhesive compositions containing a mixture of a polymerizable acrylate ester monomer and a peroxy polymerization initiator employed with a primer comprising a mixture of an aldehyde-amine condensation product and a reducing activator selected from the group consisting of defined sulfur containing free radical accelerators and compounds containing an oxidizable transition metal.
U.S. Pat. No. 3,616,040 to Toback discloses peroxy-initiated cure of acrylate based compositions where the cure is accelerated by use of a condensation reaction product Of dn aldehyde and a primary or secondary amine.
U.S. Pat. Nos. 3,890,407 and 4,106,971, both to Briggs et al, disclose employment of a condensation reaction product of an aldehyde and a primary or secondary amine to cure adhesive compositions comprising a solution of chlorosulfonated polyethylene or mixtures of sulfonyl chlorides and chlorinated polymers in polymerizable vinyl monomers. Other ingredients such an an organic salt of a transition metal, a peroxy compound and a tertiary amine may also be included in the adhesive compositions.
U.S. Pat. No. 4,182,644 to Briggs et al discloses use of a condensation reaction product of an aldehyde and a primary or secondary amine to accelerate the cure of adhesive compositions comprising a polymer, a monomer, and a free-radical generator derived from an organic sulfonyl chloride and/or a chlorosulfonated polymer.
U.S. Pat. No. 3,880,956 to Skoultchi discloses anaerobic curing compositions comprising mixtures of polymerizable acrylic and substituted acrylic monomers and diazonium salts as latent polymerization catalysts therefor. The invention is directed to anaerobic, one part adhesives.
There is a recognized need in the adhesive art for adhesives which are stable to heat and stable to storage for periods of at least six months. On use, however, the cure of the adhesive must be rapid providing strong bonds within a short period of time. In the present invention the diazonium salts provide improved heat and storage stability to the adhesives as compared to adhesives employing peroxy or hydroperoxy systems. Depending largely on the diazonium salt and the monomer base selected, typical fast curing adhesives can be formulated to remain stable, i.e., not cure or lose reactivity, for periods of six months to one year. Also depending on the selection of the diazonium salt and the selection of the aldehyde-amine condensation reaction product and other components, adhesives can be formulated having a wide range of cure speeds. Thus, adhesives can be formulated within the invention having a slow, moderate (about 60-120 seconds) or fast (about 15-30 seconds) cure. The invention provides a versatility in formulating a variety of adhesives useful in specific end-use applications.